yep better ratio is more dps so no need to stick a lesser faster weap in mainhand
mainhand hits more and procs more. a weapon proc from offhand occurs about half the time it would if it were in your mainhand. proc rates are independent of weap speed and hits. if you have two weapons that are equal or near equal ratio but one has a more desirable innate and/or augmented proc stick it in mainhand.
there are some who will argue that for example: nbob auged with tacvi dmg aug instead of a don 175 dd proc aug is more dps since the dmg aug makes the ratio better. that is correct and i agree 100%. any ranger who runs a parser will tell you the same thing; except the difference for a ranger is huge compared to a bard's..but.. i prefer two stun procs from my mainhand for hate and an extra chance to stop casting over the slight dps increase you get from having the dmg aug.
ive tried just about every combination i can with dk, 2.0, nbob, cs4 augs, and tacvi dmg aug. and really the only major difference i noticed was proc dmg. this was before tss and bards getting the double attack skill so i havnt been able to try anything for a few months but personally i prefer 2.0 with 2xcs4 augs in mainhand, and dk with tacvi aug in offhand. i get tired of the graphic sometimes so sometimes i'll switch back to nbob auged with cs4 in mainhand and epic in offhand with cs4 aug and usually the 175dd fire dmg aug from don. if i had shimmer scale i would put that in it instead